A new technique for separating the oxide damage due to program/erase (P/E) cycling and of parasitic hot-hole injection due to bitline biasing in Flash memories is presented. The technique is based on an analysis of the spatial distribution of anomalous tail cells in the array subjected to P/E cycling. We show that electron and hole injection have different dependences on the number of P/E cycles, with the latter becoming the dominating mechanism for large cycling.